The present invention relates to a public telephone system comprising a public telephone set (to be referred to as a telephone set hereinafter) and a center apparatus, in which a tariff table of the telephone set is revised by tariff change designation from the center apparatus.
To change tariffs in a conventional public telephone system of this type, data such as tariffs to be revised or corresponding telephone numbers is converted into DTMF (Dual Tone Multi Frequency) signals and transmitted from a center apparatus to each telephone set at a predetermined time for change. Each telephone set receives and stores these tariff data in an internal memory. At the same time, subsequent speech communication in each telephone set is charged in accordance with tariff data of a new tariff system.
In the conventional public telephone system, when the time for change of the tariffs is reached, the tariff data to be revised is transmitted from the center apparatus to each telephone set. In this case, since the center apparatus must transmit the tariff data to a large number of telephone sets, the telephone sets cannot be simultaneously changed to a new tariff system. Therefore, during change operation of the tariffs, speech communication in a given telephone set is charged in accordance with the new tariff system while that in another telephone is charged in accordance with the old tariff system.